The present invention relates to a printer equipped with a buffer memory for the storage of input data which may be a serial impact printer, a thermal dot printer, an ink jet printer or a line printer.
Printers of the type mentioned above are generally used as output devices for computers, word processors, and the like. In such a printer, various input data exemplified by character data and space data to be printed out, and carriage return data supplied from a host system are stored sequentially in predetermined addresses of a buffer memory from the address "0" to the address "n" and, then, read sequentially therefrom to be printed out on a sheet. The input data are held in the buffer memory until carriage return data is supplied to the printer. Before the host system delivers carriage return data to the printer, the input data in the buffer memory are held therein and a busy signal is continuously fed out to the host system to reject reception of data from the host system in response to storage of carriage return data, until the address "0" (first address to store data) of the buffer memory become empty.
Therefore, where an auto-back print mode (printing in both directions) is employed to speed up the printout operation by saving the time required for carriage returns, the above-described type of printer causes the data input first to be output last so that intermediate addresses of the buffer memory may become empty during a printout operation but not the address "0". This is represented by Table 1 shown below.
TABLE 1 __________________________________________________________________________ ADDRESS 0 1 2 3 -- 250 251 252 __________________________________________________________________________ INPUT A B C D -- Z CR DATA INPUT 1 2 3 4 -- 251 252 SEQUENCE OUTPUT 251 250 249 248 -- 1 252 SEQUENCE IN BACK MODE OUTPUT 3 2 1 EMPTY -- EMPTY 4 SEQUENCE AMID BACK MODE __________________________________________________________________________
Thus, in the prior art type described, the busy signal is continuously fed out to the host system until all the data stored in the buffer memory are processed in the back-print mode. The slower the operation of the printer, the longer the duration of the busy signal is.
Meanwhile, a host system is generally constructed to determine that a printer associated therewith has failed and, thereby, interrupt the job, when the busy signal from the printer has lasted a predetermined period of time such as 2.5 seconds or 4 seconds. As a result, even when the printer sends out the busy signal to simply indicate that auto-back printing is under way, the host system identifies the situation as a failure in the printer to cut off the job.